[Janz's juvenile myoclonic epilepsy: a little-known frequent syndrome. A study of 85 patients].

BACKGROUND

Juvenile myoclonic epilepsy (JME) constitutes 10% of all epilepsies. Despite this syndrome being well defined, its diagnosis is usually delayed. The aim of this study was to analyze the clinical and electroencephalographic characteristics to facilitate guidelines to contribute to its recognition.

METHODS

From January 1986 to July 1993 the clinical and EEG data of 85 patients with JME were prospectively studied. In 68 cases (80%) the polygraphic study of sleep was also analyzed during a nap period.

RESULTS

The series included 44 males and 41 females of a mean age of 28 years (range: 13-63). Fifty-six percent of the cases showed family history of epilepsy and/or febrile convulsions. All the patients had myoclonic crisis with the age of 15 being the mean age of initiation (range: 8-27). Eighty-seven percent also had generalized tonic-clonic crisis and 18% typical absences. Myoclonias were presented daily up the administration of adequate treatment in 60% of the cases with 21% having myoclonic status. The mean interval from the initiation of the myoclonic crisis to diagnosis of JME was of 10.6 years. On monotherapy with valproic acid and following a mean follow up period of 23.8 months, 86% of the patients remained free of crisis. Nonetheless, the rate of recurrence was 100% in the 19 patients who discontinued the treatment. Surveillance EEG was normal on some occasion in 88% of the cases. The most characteristic paroxysms were the following: wave-point at 4-5 Hz and generalized rapid wave-polypoint. Light stimulation provoked a paroxysmal response in one third of the cases. Sleep EEG was abnormal in all the patients. An activation of the paroxysms during non-REM sleep in 78% of the cases and on waking up in 25%.

CONCLUSIONS

Juvenile myoclonic epilepsy is a well defined syndrome. Its diagnosis is based on directed anamnesis allowing myoclonic jerks to be collected which often remain unperceived, and EEG exploration with sleep tracing in which the characteristic outbreaks of wave-point or generalized rapid wave-polypoints may be discovered.